/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

package org.apache.harmony.luni.util;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * This class implements a password-protected input stream. The algorithm used
 * for protection is a Vigenere (repeated-key) cipher. The encrypted data is the
 * result of <original data> XOR KEYKEYKEY...
 */
public class PasswordProtectedInputStream extends FilterInputStream {

	private final byte[] password; // Password to use to decrypt the input bytes

	private int pwdIndex; // Index into the password array.

	/**
	 * Constructs a new instance of the receiver.
	 * 
	 * @param in
	 *            The actual input stream where to read the bytes from.
	 * @param password
	 *            The password bytes to use to decrypt the input bytes
	 */
	public PasswordProtectedInputStream(InputStream in, byte[] password) {
		super(in);
		this.password = password.clone();
	}

	@Override
	public int read() throws IOException {
		int read = in.read();
		if (read >= 0) {
			read ^= password[pwdIndex];
			pwdIndex = (pwdIndex + 1) % password.length;
		}
		return read;
	}

	@Override
	public int read(byte b[], int off, int len) throws IOException {
		final int read = in.read(b, off, len);
		if (read > 0) {
			final int lastIndex = off + read;
			for (int i = off; i < lastIndex; i++) {
				b[i] ^= password[pwdIndex];
				pwdIndex = (pwdIndex + 1) % password.length;
			}
		}
		return read;
	}

	@Override
	public long skip(long n) throws IOException {
		final long skip = super.skip(n);
		pwdIndex += skip;
		return skip;
	}
}
